Lunar Composition by Scintillation Spectroscopy

Information on the composition of the moon and its past history is being sought through measurements of the spectrum of the gamma rays emerging from the lunar surface. The detector is a 3 × 3 in. CsI-plastic scintillator phoswich feeding a 32-channel analyzer weighing 5 pounds. Energy range is to 3 Mev; in-flight calibration is provided by a small Co-57 and Hg-203 source fixed to the detector. Energy resolution is 12 ± 2 per cent at 0.66 Mev. The spectrometer, and indeed the entire spacecraft, is biologically sterile. The spectrometer aboard Ranger 3 (launched January 26, 1962; missed the moon by about 20,000 miles) transmitted back spectra currently being studied; Rangers 4 and 5 are repeats scheduled for later in 1962.